The control systems known at present and which may be placed in the back cover of a case are numerous. They may, for instance, comprise movable or stationary components which react to pressure (push-buttons, membranes associated with an internal electrical contact, piezo-electric keys). Arrangements may also be provided which operate according to a purely electrical principle (capacitive keys, simple insulated contacts which are grounded by touching with the finger or by connecting them to the watch case by means of a metallic object, contact pairs which may be coupled between themselves). Finally, there may also be cited electro-magnetic arrangements which comprise a relay housed entirely within the watch which may be actuated from the exterior by employing a small magnet.
Actually, this possibility of placing the control system of a watch behind the latter has up to the present been only rarely employed. However, it would quite often enable simplification of the fabrication of the movement, of the case or of the control mechanisms themselves, to facilitate their assembly or simply to resolve the problems associated with water tightness. For instance, in very thin watches, i.e. 3 mm or less, it is very difficult to make one or several holes in the caseband to accommodate a time setting stem or to house push-buttons while providing the necessary sealing means without risk of rendering such watches very fragile. Since moreover for the most part top quality watches are concerned, it is out of the question to locate such visible mechanisms as push-buttons or fixed electrical contacts in front of the watch and even arrangements still little employed such as photo diodes or capacitive keys on the crystal, which incidentally are difficult to adjust and necessitate complex electronic circuits, are only rarely suitable. The solution obtained by placing these control arrangements on the back-cover of the watch would thus in such cases be very advantageous. However, resort is made thereto only when truly obliged to do so and this for the same reasons that utilization for certain styles of watches is avoided where even the presence of a stem becomes unattractive and where, consequently, it would be likewise interesting.
One of the reasons for avoiding this solution is that with certain exceptions, as with pendant watches, it obliges the watch wearer to put it down when he wishes to undertake an adjustment or otherwise to control it. In reality, this does not represent a serious difficulty since it is not infrequent that one also does the same thing with a watch provided with a classical system of correction on finding that manipulations are easier thereby.
The other reason is that generally, the wearer experiences far more difficulties in setting the time and in some cases controlling other functions than if the control mechanism or mechanisms were placed in front of the watch or on the side. Effectively, in this case he must begin by looking at the back of the watch to see where is to be found the mechanism which must be actuated and according thereto, place the end of the finger or a suitable object on or close to the latter. Without so doing, he would risk groping for considerable time and, if there are several mechanisms, to be mistaken. Next he must turn over the watch to observe the modifications of the display while he acts on the mechanism and it is entirely possible that at a given moment including when he turns the watch over, his finger or the object in question slides on the back cover or is removed therefrom. It remains then to recommence the same manoeuvre.
This difficulty is much more bothersome than the preceding one and what the invention has as purpose is not to suppress it for this is almost impossible, but to minimize it.
In other words, the purpose of the invention is to seek to render a control system situated on the back cover of a watch case as practical to employ as those which are found on the side or in front, the latter being likewise, from this viewpoint, not always perfect.
This purpose is attained owing to the fact that when a control system is fixed to the back cover of a watch in conformity with the invention, this back cover is provided with positioning means which determine approximately at least the place where the means external to the case must be placed in order to be able to actuate the mechanism in question.
Furthermore, in the preferred method of carrying out the invention, the back cover of the case is likewise provided with means for guiding these external actuating means towards the positioning means.
When the watch likewise comprises a bracelet with a closing element, it is advantageous to be able to employ a portion of this element as means for actuating the control system since one has such element permanently and immediately at hand. Consequently, in this case, the positioning means and eventually guide means are preferably adapted to the form and to the dimensions of this portion of the closing element and the control mechanism is chosen in a manner to be capable of actuation thereby.